The present invention relates generally to the field of orthopedic medicine and more specifically to an improved cast formed of a tubular fabric structure impregnated or coated with a moisture-curable plastic material, a tubular cast assembly which includes the tubular cast and its packaging, a method for constructing such an improved tubular cast assembly and a method for applying a cast to a body part to be immobilized. The product includes structural features which permit the cast to be easily removed without the use of a cast saw when immobilization of the limb is no longer required or the cast needs to be changed.
Medical bandages for use in the treatment of injuries, such as broken bones requiring immobilization of a body member, are generally formed from a long strip or strips of fabric or scrim material, referred to as cast tape, impregnated with a substance which hardens into a rigid structure after the strip or strips have been wrapped around the body member. The hardening substances traditionally used in carrying out this procedure are plaster-of-paris and polyurethanes.
Conventional practice, which is still very common, has been to fabricate a cast or splint upon an injured limb by initially applying to the limb a protective covering of a cotton fabric or the like and then overwrapping the covering and the underlying body part with a woven cloth impregnated with plaster-of-paris or polyurethane which has been wetted by dipping in water immediately prior to application. This practice is still in widespread use but possesses several significant disadvantages.
The above-described application procedure is messy and time consuming. Several components are required and considerable skill is necessary. If too little cast tape is used to fabricate the plaster cast, breaking or "hinging" at stress points can occur as the patient wears the cast over a period of time. This, of course, requires replacement of the cast. It is common to make a plaster cast heavier than it really needs to be in order to insure against breaking. This practice creates its own problems, including greater weight for the patient to carry, greater heat and moisture retention and greater use of materials.
In order to alleviate these disadvantages of the conventional application procedure for plaster-of-paris casts and splints, unitary splinting materials have been devised and are disclosed in, for example, U.S. Pat. Nos. 3,900,024, 3,923,049, and 4,235,228. All of these patents describe a padding material with a plurality of layers of plaster-of-paris impregnated cloth. Such unitary splinting materials are not as messy and can be applied more quickly but still suffer from a number of disadvantages inherent in plaster-of-paris cast materials. All plaster-of-paris splints have a relatively low strength to weight ratio which results in a finished splint which is very heavy and bulky. Plaster-of-paris splints are slow to harden, requiring 24 to 72 hours to reach maximum strength. Since plaster-of-paris breaks down in water, bathing and showering are difficult. Even if wetting due to these causes can be avoided, perspiration over an extended period of time can break down the plaster-of-paris and create a significant problem with odor and itching.
A different way of forming a cast is disclosed in U.S. Pat. Nos. 4,411,262 and 4,502,479. The casting materials disclosed in these patents comprise a flexible fabric impregnated with a moisture-curing resin. The impregnated fabric is enclosed in a moisture-free, moisture-impervious package where it is stored until immediately prior to use. Compared to plaster-of-paris, these products are extremely lightweight, have a very high strength-to-weight ratio and can be made relatively porous, permitting a flow of air through the casting material. Prior art moisture-curing systems include a package within which is contained a plurality of layers of fabric, such as fiberglass, impregnated with a moisture-curing resin. The layers of fabric are applied in layers much as with plaster coated strips. Judgment and experience is required to apply the layers of fabric in manner which results in a cast which will securely immobilize the body part, provide greater strength in those areas of the cast where necessary, and yet will be as light weight as practical in order that the patient can safely wear the cast for an extended time.
From the above discussion, both the conventional plaster-of-paris casting method and the more recent moisture-curable resin casting method possess both advantages and disadvantages. On the one hand, plaster-of-paris casts are bulky, heavy and difficult to apply whereas moisture-curable resin casts are lightweight, durable and relatively easy to apply. On the other hand, plaster-of-paris can be very easily stored and used as needed since it has a relatively long shelf life so long as it is not completely wetted, whereas the moisture-curable resins are very sensitive to the presence of even minute amounts of moisture. This requires that either the materials be packaged in a wide variety of different shapes and sizes or unused portions be discarded, generating a substantial amount of waste and increasing the effective cost of the product. This invention combines the advantages of both plaster-of-paris and moisture-curable resin systems while avoiding their respective disadvantages by providing a tubular cast which is already formed and ready to place on the body part, and which is easily applied and removed.
In addition, the invention described below allows various parts of the cast to provide different degrees of strength. For example, a portion of the cast to be positioned around the smaller body part, such as the ankle or wrist, will preferably be stronger than elsewhere in accordance with good medical practice.
As used in this application unless otherwise explained by context, the terms "cast" and "tubular cast assembly" refer to the finished structure as it exists on the body part to be immobilized. The term "cast tube" refers to the outer tube which is treated with a moisture-curable reactive system and then placed over a previously applied sleeve. The term "tubular cast product" refers to the cast tube and the moisture impervious packaging within which the cast tube is stored until just before use.
Tubular casts are known in the prior art. However, whether formed into a tube on the limb by applying numerous strips of material, or pre-formed and slipped onto the limb in tubular form, the cast must still be removed using a cast saw. A cast saw has a serrated blade which looks to the patient as if it is rotating in the manner of a circular saw. Many patients, particularly children, become frightened at the prospect of their cast being removed by the saw. In fact, the cast saw blade is not particularly sharp, and the blade oscillates with a short periodicity so that there is little danger of the patient being injured. However, the apparent danger of the saw, particularly the noise of the saw, outweighs the reality of the safety of the saw in the minds of many patients.
Cast saws have other disadvantages as well. They are noisy, require maintenance and, of course, as subject to damage, wear and blade replacement. Removal of a cast with a cast saw generates airborne fiberglass and/or plaster dust which is messy and is sometimes perceived as hazardous products. The cast according to this invention may be removed with or without a cast saw.